The invention relates to an apparatus for plasticizing thermoplastic synthetic plastics material, in particular synthetic plastics scrap material, comprising a screw bearingly supported within a housing, to which screw the material to be plasticized is supplied through a feed opening of the housing, said screw conveying the synthetic plastic material to an exit opening for the plasticized synthetic plastics material disposed in axial distance from the feed opening, a comminuting means for the syntectic plastics material being attached to the feed opening, which comminuting means comprises comminuting tools disposed on two shafts which extend parallel to each other and preferably parallel to the axis of the screw and are driven in opposite directions, which comminuting tools convey the comminuted synthetic plastics material into the feed opening of the screw housing, each of the comminuting tools being provided with teeth acting on the synthetic plastics material supplied between the shafts.
Within such apparatus there is the problem that the synthetic plastics material which in most cases is supplied in form of scrap material, must be comminuted but nevertheless must be reliably supplied to the screw without blocking the revolution of the comminuting tools and, respectively, or the screw. The known proposals were not satisfying with this respect.
It is the task of the invention to improve an apparatus of the initially described kind so that the problem mentioned above is solved satisfactory, that means that on the one hand the supplied synthetic plastics material is effectively comminuted and that on the other hand the comminuted synthetic plastics material is reliably taken along by the screw and is plasticized and is discharged through the exit opening without that the shafts carrying the comminuting tools or, respectively, the screw are blocked. The invention solves this task by the features that the shafts are driven with different speeds of revolution, the direction of revolution of the shaft running with greater speed being opposite to the direction of revolution of the screw, that the comminuting tools are disposed axially spaced apart from each other on the shaft, the orbits of the teeth of the comminuting tools of the two shafts overlapping each other, when seen in axial direction of the shafts, and that at least on the shaft running with greater speed spacer disks having a circular periphery are disposed between neighboring comminuting tools, stationary filter elements engaging between the comminuting tools of this shaft and extend with their flanks facing the gap between the shafts tangentially with respect to the periphery of the spacer disks of this shaft. The shafts running with different speeds effectively comminute the supplied synthetic plastics material by means of the teeth of the comminuting tools, in as much, so to speak, neighboring comminuting tools frictionally engage each other. Thereby, the comminuted synthetic plastics material is reliably freed from the comminuting tools and is not, as this was frequently the case within the known proposals, conveyed in a circle around the respective shaft. This is also supported by the tangentially extending flank of the stationary knife which, so to speak, strips off the syntectic plastics material elements which have proceeded in radial direction inwardly to the spacer disks from the spacer disks and also from the substantially disk-shaped comminuting tools. Thereby a stuffing component which is directed substantially tangential with respect to the shaft running with greater speed is exerted onto the comminuted synthetic plastics material, which force component tends to press the syntectic plastics material in direction towards the screw and into the revolutions thereof. Particularly favorable results are obtained if these flanks extend also tangentially with respect to the wall of the feed opening, since in such a manner it is ensured that the synthetic plastics material supplied to the screw by the two shafts is continuously taken along.
From the EP-A-140,869 an apparatus for comminuting scrap material, above all burnable scrap material is known in which the comminuted material is supplied to a screw press for briquetting. For comminuting the scrap material, comminuting tools are provided on two oppositely driven shafts that extend parallel to each other and parallel to the axis of the screw, which tools convey the comminuted scrap material towards the screw. The comminuting tools have teeth acting on the scrap material which is supplied between their shafts and are disposed in axial distance from each other on the shafts so that the orbits of the teeth of the two shafts overlap each other. Between neighboring comminuting tools spacer disks having a circular periphery are provided and stationary knives extend between the comminuting tools of the shafts.
Further it is known (DE-A-2,450,936), (DE-A-3,430,087), to drive two cutter shafts disposed parallel to each other of an apparatus for disintegrating bulky goods or, respectively, for comminuting scrap material in opposite directions and with different speeds.
According to a preferred embodiment of the invention both shafts are provided with circular spacer disks disposed between the disk-like comminuting tools, to which spacer disks the flanks of the stationary knives extend tangentially and symmetrically with respect to the central plane between the two shafts, and preferably those peripheral sections of the stationary knives which adjoin these flanks in direction of revolution of the shafts extend following the periphery of the spacer elements. Thereby the favorable effects mentioned above are ensured for both shafts of the comminuting means.
Further, investigations have shown that it is favorable to dispose a certain clearance between the two shafts of the comminuting means and the screw. Within the spirit of the invention, such a clearance can be constituted by the feature that the orbit of the tips of the teeth is spaced apart from the periphery of the screw volutions in a distance that amounts to 0.5 to 1.5 times the distance by which the orbit of teeth tips is spaced apart from the periphery of the spacer disks. Thereby, blockings of the revolving elements are still better avoided.
For the purpose to avoid that the comminuted synthetic plastics material taken along by the screw revolves together with the revolving motion of the screw and thereby is not conveyed effectively towards the exit opening, according to a further embodiment of the invention at least in the region of the feed opening protrusions or grooves are provided in the wall of the housing of the screw disposed spaced apart from the periphery of the screw volutions, which protrusions or grooves preferably extend in axial direction of the screw. These protrusions or grooves, respectively, prevent that the synthetic plastics material runs together with the screw.